Giganto characters

alex duncan (
3 Aug 1995 01:05:39 GMT


I just had another look into your database (actually, I downloaded it and
played w/ it some). I'm disturbed by the number of character states that
you have entered for Gigantopithecus. For example:

incisive canal: overlap (pongo)
maxillary sinus: absent
brow ridge: none
glabella: minor
facial shape: muzzle
cranial capacity: various character states
brain case wall: thin
carotid artery entry: ventral
vault profile: primitive (small)
basicranial flexion: absent
separate os centrale: present
curved metacarpals: present
FM [foramen magnum?] placement: quadrupedal
prehallux: absent
etc. etc.

I wonder how much of an impact these have on your placement of
Gigantopithecus? I realize that we really do "know" what a lot of these
character states are (although we shouldn't make these assumptions about
the ones i've listed above), but when you make these assumptions in your
data base you jump ahead in the process one step. For example, you have
"maxillary sinus: absent" as a character/state. My impression is that
there are no Giganto fossils that preserve this anatomy. You may have
good reasons for assuming the maxillary sinus is absent, but that should
come as a result of your cladistic exercise, and not as an assumption you
begin with.

It would be interesting to take your database and remove all data that
are not concretely supported by the fossil record (even stuff like "tail:
absent" for Giganto). And then see what comes out of it. We all know
damn good and well Giganto didn't have a tail, but it biases your
results. I suspect the result will be a lot less confidence in the
placement of some taxa, but that is a price that has to be paid to do
good science.

I've agonized over this myself a great deal. We teach an intro course in
which we have students use MacClade to do an exercise w/ representative
groups of modern primates. We have to keep characters simple, so the
students will have some understanding of them. We throw in a few
interesting fossil taxa (Siva, Australopithecus afarensis, Proconsul) and
ask the students to predict character states for them after completing
the exercise.

We can be pretty confident that Siva didn't have a tail, because its a
'noid, and 'noids don't have tails. But we don't have any fossils that
bear on the issue. So we leave a "?" in our file for the character
state, and ask students to "predict" for us whether or not Siva had a
tail, based on its position in the cladogram.

To get back to the case of Giganto, you're assuming that it has a lot of
character states that are similar to those seen in Pongo and Siva, even
though these parts aren't represented in the fossil record. I feel
confident that those assumptions are effecting the position of Giganto in
your cladogram.

Alex Duncan
Dept. of Anthropology
University of Texas at Austin
Austin, TX 78712-1086